Captain Poindexter was killed when a water scooter driven by his 26-year-old son Zachary struck the back of the scooter the former astronaut was driving.

"They were both moving and for some reason Capt. Poindexter stopped his watercraft and Zachary for some reason didn't see him stop," said Stan Kirkland, a spokesperson for the Florida Fish and Wildlife Conservation Commission. "Zachary's watercraft went up and struck Capt. Poindexter."

The two-time space shuttle astronaut was on the WaveRunner with his 22-year-old son Samuel, who was also ejected from the water craft after the collision, but was not injured.

Poindexter was pulled from the water and taken to the beach where friends attempted to revive him. He was transported via helicopter to Baptist Hospital where he died from his injuries, said Kirkland.

Although all three men were wearing law-required law jackets, Kirkland noted that investigators were involved.

"It's technically still under investigation until our report is complete," said the spokesperson, calling the incident "a terrible tragedy."

The accident occurred between Gulf Breeze and Pensacola Beach in Florida's Panhandle where the Poindexter family had been vacationing and where they had many ties. His wife, Lisa, is from Gulf Breeze, and Poindexter reported to flight training in Pensacola after college.

The former astronaut's first mission was in 2008 as a pilot aboard the Atlantis to install the Columbus laboratory at the International Space Station. He also commanded Discovery's second-to-last flight in April 2012 on a mission to resupply the space station.

Poindexter is the son of former U.S. National Security Advisor John Poindexter, who served during the Reagan Administration.

"He was a passionate, caring, and selfless individual who will be missed by all," said Leland Melvin, a former astronaut and current associate administrator for NASA in a statement released by the agency.

The former astronaut, nicknamed "Dex," is being mourned on Twitter by fans and colleagues alike.

"He was a talented, courageous Navy veteran with gifts," wrote astronaut Greg Johnson via Twitter. "Dex was a lovable guy with a strong work ethic."

Astronaut Jack Fischer wrote, "Here's a toast… to a great astro, a great Naval Officer, & a great man- Captain Alan Poindexter- you'll be missed sir."